Guidelines that directed less use of adjuvant radiation therapy for older women with early stage breast cancer had minimal impact, even among the oldest women and those with shorter life expectancies, researchers found.

A 2004 study randomly assigned women 70 years or older with stage I estrogen receptor-positive disease and a tumor size less than 2 cm to receive surgery and tamoxifen, with optional radiation. Radiation did not improve 5-year overall or disease-free survival, nor did it decrease the rate of mastectomy for recurrence.

Results prompted the National Comprehensive Cancer Network to change its guidelines in 2005 to make adjuvant radiation optional.

To assess whether physicians followed the guidelines, researchers looked at Surveillance, Epidemiology, and End Results data to assess the use of adjuvant radiation in women 70 years and older diagnosed with stage I breast cancer from 2001 to 2007.

Results appeared in the March 5 issue of the Journal of Clinical Oncology. Of nearly 13,000 Medicare beneficiaries (mean age, 77.7 years), 76.5% received radiation, approximately 79% before the guidelines compared with 75% after (adjusted relative risk, 0.97; 95% confidence interval [CI], 0.95 to 0.98).

Although use of radiation was lower after the trial within all strata of age and life expectancy, the magnitude of this decrease did not differ significantly by strata. For instance, among patients with life expectancy less than 5 years, radiation use decreased by 3.7%, from 44.4% before the guidelines were published to 40.7% after the guidelines. Among patients with life expectancy more than 10 years, radiation use decreased by 3.0%, from 92.0% to 89.0%.

"Although the U.S. government has invested significant resources in comparative effectiveness research studies, our analysis suggests that practice patterns may not necessarily change on the basis of the results of such studies," the authors wrote.

Reimbursement may influence physicians to continue old habits, and also, the "shiny new toy" theory may hold, in which randomized controlled trials are more likely to influence physicians if they introduce a new technology, rather than take one away.

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